Optimization of triple-pressure combined-cycle heat and power plants integrated with thermal desalination processes

MANASSALDI, JUAN I.; MOROSUK, TATIANA; MUSSATI, MIGUEL C.; MUSSATI, SERGIO F.; SCENNA, NICOLÁS J.; MANASSALDI, JUAN I.; MOROSUK, TATIANA; MUSSATI, MIGUEL C.; MUSSATI, SERGIO F.; SCENNA, NICOLÁS J.

Cracovia

Conferencia; CPOTE 2020 - 6th International Conference on Contemporary Problems of Thermal Engineering; 2020

Silesian University of Technology and AGH University of Science and Technology

This work deals with the optimal synthesis, design, and operation of an integrated triple-pressure steam-reheat combined-cycle heat and power (CCHP) plant with a multiple-stage flash (MSF) desalination process to simultaneously generate electricity and produce freshwater from seawater.The study is performed using mathematical programming techniques and a generalized gradient-based optimization algorithm. A superstructure-based representation of the heat recovery steam generator (HRSG) of the CCHP embedding simultaneously several attractive candidate structures of the HRSG was proposed and a mixed-integer nonlinear programming (MINLP) model was derived from it.The model is developed in such a way that the number of the pressure levels in the HRSG is also included to the set of optimization variables. Series, parallel, and combined series-parallel heat exchanger arrangements as well as steam reheating are allowed. Therefore, depending on the demands of electrical power generation and freshwater production rate, an integrated process with HRSG structures involving three, two, or one pressure levels can be obtained as the optimal structure since the heat exchangers can be selected or removed from the superstructure accordingly. The CCHP plant and MSF system are modelled based on first-principle models of the involved equipment.In this work, the maximization of the ratio between the freshwater production rate and total heat transfer area required in the HRSG is performed, while satisfying a fixed, specified electrical power generation level. An existing dual-purpose desalination plant with a 1P-HRSG, located in Kuwait, is used as a reference case for model validation and result comparison purposes. A result showed that the freshwater production rate is increased by 4.6% and that the heat transfer area required in the HRSG is reduced by 13.9% if the 1P-HRSG is replaced with a 3P-HRSG in the integrated CCHP-MSF system.